This invention relates to a lens fixture, more particularly a fixture for removably attaching a lens at an apparatus.
In the first place, the invention is intended for fixing a lens in a projector; it is, however, clear that it can also be applied in other devices.
Already, different kinds of lens attachment systems are known. A first classical system consists of a screw thread connection which, however, shows the disadvantage that it is cumbersome to attach the lens, unscrew it, respectively. A second classical system consists of a bayonet coupling, whereby the lens has to be inserted axially into a seat and subsequently has to be rotated over a well-defined angle. Such bayonet coupling, however, does not offer a large rigidity, which, in the first place, forms a disadvantage with large lenses, as these, due to the influence of their weight, are no longer kept at their location in an efficient manner.
Apart therefrom, other lens attachment systems are known, whereby use is made of a so-called lens port, or of fins situated around the lens. These systems show the disadvantage that they are rather cumbersome in use.
From the patent documents U.S. Pat. No. 4,249,799, U.S. Pat. No. 4,062,030 and GB 1.590.752, fixtures are known, amongst others, lens fixtures, with radially movable pressing elements, whereby in coupled condition also a permanent axial pressing force is created. The systems disclosed in these documents apply lever systems and the like, which have the disadvantage that they take up a lot of space. Moreover, they are provided with helicoidal springs, the tension force of which mostly is rather limited.
The present invention aims at a lens fixture which allows to attach a lens in an efficient manner very stable in an apparatus, even in the case of large lenses, more particularly lenses with a weight of several kilograms, whereby this lens can be attached in the apparatus, as well as removed therefrom, in a smooth manner.
To this aim, the invention relates to a lens fixture for removably attaching a lens at an apparatus, which consists at least of, on one hand, a seat at the lens or at an adapter piece and, on the other hand, an attachment mechanism at the apparatus, which mechanism at least is composed of a carrier structure with an opening for providing the lens or adapter piece therein, and an elastically working pressing system comprising one or more substantially radially working pressing elements, which pressing system can cooperate with said seat of the lens, the adapter piece, respectively, and, in coupled condition of the lens or the adapter piece, exerts a permanent axial pressure force onto this latter, with the characteristic that the lens fixture comprises pressing elements formed by spring wire.
By using one or more radially movable pressing elements, a very efficient clamping attachment is obtained.
Due to the permanent axial pressing force, the important advantage is created that the lens, once clamped, always remains in the same position and no longer can shift in axial direction.
By applying spring wire for the pressing element, pressing elements, respectively, in other words, applying hereto wire-shaped elements which, for example, are made of spring steel, amongst others, the advantages are obtained that said elements take up little space and therefore easily can be mounted around the opening in which the lens is provided, that they can be fixed in the carrier structure in a simple manner, for example, by providing them in a small seat, and that, notwithstanding their small dimension, can provide rather a large tension.
Preferably, the spring wires are positioned substantially tangential around the lens, or at least around the opening in which the lens is provided. Hereby, each respective spring wire, at least in active condition, substantially is held in the proximity of two extremities and therefore can be bent out elastically in the middle, according to a direction radial to the opening in which the lens is provided.
Preferably, the seat at the lens consists of one or more recesses. In the most preferred form of embodiment, this seat extends along the entire circumference of the lens.
Practically, it is preferred that the seat shows a contact surface which extends in an inclined manner in respect to the axial direction of the lens. As a result of the effect of the radially movable pressing element, the radially movable pressing elements, respectively, onto each pertaining contact surface, in this way the creation of a radial as well as an axial force component is obtained in a constructively simple manner, as a result of which the lens is enclosed laterally and held, as well as pressed-on axially, preferably against stop parts especially provided to this purpose.
According to a particular characteristic of the invention, the aforementioned contact surface extends in respect to the vertical at an angle which is smaller than the frictional angle determined by the materials and the surface condition of, on one hand, said contact surface and, on the other hand, the pressing element cooperating therewith. In this manner, a self-braking effect is created, as a result of which this lens, regardless of the weight thereof, will not be loosened by itself.
In practice, the aforementioned angle will be smaller than 30xc2x0 and even better will be of the order of magnitude of 15xc2x0.
In a preferred form of embodiment, several pressing elements are provided along the circumference, which, for example, are distributed along the circumference in a rotationally symmetric manner. In the most preferred form of embodiment, this will be three or four in number. By using at least three pressing elements, a well-balanced clamping will be guaranteed, whereas by using preferably maximum four pressing elements, a constructively rather simple mounting of these pressing elements in the carrier structure can be provided for.
According to another preferred characteristic of the invention, the unit has means which allow a snapping-on of the lens in the carrier structure against the force exerted by the elastically working pressing system. As a result of this, the lens can be provided in the apparatus in a simple manner by sliding it into the aforementioned opening of the carrier structure, whereby it then automatically becomes attached.
Although it is not excluded to realize the lens fixture in such a manner that the lens can be removed exclusively by means of a tool or of another accessory, it is preferred that said attachment mechanism comprises a control mechanism with which the pressing element, the pressing elements, respectively, can be brought into at least two positions, to wit an inactive position whereby the lens can be removed from said opening, and an active position whereby, in any case, if the lens is provided in the attachment mechanism, the pressing element, the pressing elements, respectively, hold the lens and, more particularly, exert a force upon the lens. Due to the control mechanism, the lens can be loosened from said carrier structure in a particularly simple manner, such by operating the control mechanism in a suitable manner and subsequently sliding the lens axially out of the carrier structure.
In a practical form of embodiment, the control mechanism then will comprise a movable element, provided with means for the displacement thereof, whereby this movable element cooperates with the movable pressing element, pressing elements, respectively, and can move the pressing element, pressing elements, respectively, radially outward, such that the lens can be freely removed from the opening.
According to a particular aspect, which, according to the present invention, is not limited to pressure elements consisting of spring wires, but also can applied with lens fixtures having pressing means realized in a different manner, the control mechanism comprises elastic means which force the control mechanism into a well-defined position, as well comprises a locking system with which it can be locked, against the force of said elastic means, in a position in which the pressing element, pressing elements, respectively, are in one of the aforementioned positions, either the inactive position or the active position. With a locking in inactive position, the advantage is obtained that the control mechanism can be permanently put into inactive position, as a result of which the operator has both hands free for removing the lens, which is particularly advantageous in case of heavy-weight lenses of several kilograms. With a locking in active position, it is obtained, amongst others, that a careless uncoupling is prevented.
Other preferred characteristics are described in the detailed description and the dependent claims. In general, thanks to the invention described in the aforegoing, the following advantageous features are obtained:
a perfect positioning of the lens against the apparatus, without play;
a very rigid connection, suitable for heavy lenses;
a simple lens body, as the housing of the lens can be manufactured exclusively by lathe work;
a lens fixture which allows that the lens is not bound to an orientation, although, according to a variant, it is possible to provide such orientation;
the insertion of the lens can be performed with two hands, as no separate operations have to be performed;
the removal of the lens is very simple, as well;
the unit does not comprise any delicate or fragile parts and can easily be made of wear and tear-resistant materials;
the fixture is self-centering.
It is noted that, according to the invention, said seat either is provided at the housing of the lens itself, or at an adapter piece in which a lens can be attached.
Evidently, the invention also relates to lenses and adapter pieces equipped with special provisions, in particular with a seat such as described in the aforegoing, which allow that such lens or adapter piece can be attached in an apparatus by means of a lens fixture as described in the aforegoing.
It is also evident that the invention also relates to apparatuses provided with an attachment mechanism as described in the aforegoing. According to the invention, by the term xe2x80x98apparatusxe2x80x99 a complete apparatus as well as a part of an apparatus as well as a constructive part which can be attached at an apparatus, such as a projector or such, has to be understood.